Name ____________________________________________________
Complete the following table using the fossil timeline illustration and then answer the questions on the back on this page.
Organism Jaw order Palate order Fossil Record order
Sphenacodontid 1 or 2
Biarmosuchian 2
Theriodont 3 or 4 1 or 2
Procynosuchus 4 2
Thrinaxodon 5 3
Probainognathus 6
Ictidosaur 7
8 4 Morganucodon

What do you conclude about hypothesis 1, mammals and reptiles share a common ancestor, based on the evidence? Explain.
Include consideration of the three predictions of hypothesis 1:
A. we will find intermediate fossil species
B. we will find a sequence of fossils from reptile-like characteristics to mammal-like characteristics
C. we will find a chronological order to the fossils, with reptile-like species being oldest to mammal-like species being youngest
What do you conclude about hypothesis 2, mammals and reptiles do NOT share a common ancestor, based on the evidence? Explain.
Include consideration of the three predictions of hypothesis 2:
A. we will NOT find intermediate fossil species
B. we will NOT find a sequence of fossils from reptile-like characteristics to mammal-like characteristics
C. we will NOT find a chronological order to the fossils, with reptile-like species being oldest to mammal-like species being youngest